Bacteriophage T4 RNA ligase joins RNA and DNA strands in the absence of template direction. Gene 63 codes for RNA ligase and the enzyme is required for tail fiber attachment. We will probe the mechanism of this reaction and search for additional functions of the enzyme. RNA ligase is a valuable reagent for synthesis of defined nucleic acids. However, the yield in one of its reactions, the intermolecular ligation of single-stranded DNA, is not now satisfactory and we will optimize the reaction conditions. We hope to assay, purify, and characterize the enzyme(s) responsible for the integration of translocatable sequences; this reaction we expect will be like RNA ligase in that joining will occur in the absence of a base-paired strand.